From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Nathan Lynch <ntl@pobox.com>
Cc: linuxppc-dev@ozlabs.org, Paul Mackerras <paulus@samba.org>
Subject: Re: [PATCH] fix gettimeofday vs. update_gtod race
Date: Thu, 17 Aug 2006 01:48:54 +0200 [thread overview]
Message-ID: <1155772134.11312.119.camel@localhost.localdomain> (raw)
In-Reply-To: <20060811204105.GK3233@localdomain>
On Fri, 2006-08-11 at 15:41 -0500, Nathan Lynch wrote:
> + /* Sampling the time base must be done after loading
> + * do_gtod.varp in order to avoid racing with update_gtod.
> + */
> + rmb();
> + tb_ticks = get_tb() - temp_varp->tb_orig_stamp;
The barrier isn't necessary and the race not completely closed imho... I
need to think about it a bit more closely but what about instead just
check if tb_ticks goes negative, and if yes, just do get_tb() again ?
That might be faster than having a sync in there and should still be
correct.
> temp_tb_to_xs = temp_varp->tb_to_xs;
> temp_stamp_xsec = temp_varp->stamp_xsec;
> xsec = temp_stamp_xsec + mulhdu(tb_ticks, temp_tb_to_xs);
> @@ -464,7 +469,7 @@ void do_gettimeofday(struct timeval *tv)
> tv->tv_usec = usec;
> return;
> }
> - __do_gettimeofday(tv, get_tb());
> + __do_gettimeofday(tv);
> }
>
> EXPORT_SYMBOL(do_gettimeofday);
>
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@ozlabs.org
> https://ozlabs.org/mailman/listinfo/linuxppc-dev
next prev parent reply other threads:[~2006-08-16 23:49 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-08-11 20:41 [PATCH] fix gettimeofday vs. update_gtod race Nathan Lynch
2006-08-16 23:48 ` Benjamin Herrenschmidt [this message]
2006-08-17 0:18 ` Nathan Lynch
2006-08-17 0:27 ` Benjamin Herrenschmidt
2006-08-17 20:47 ` Nathan Lynch
2006-08-21 21:25 ` Nathan Lynch
2006-08-21 21:43 ` Benjamin Herrenschmidt
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1155772134.11312.119.camel@localhost.localdomain \
--to=benh@kernel.crashing.org \
--cc=linuxppc-dev@ozlabs.org \
--cc=ntl@pobox.com \
--cc=paulus@samba.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).